Microbiology Exam IV Study Notes: Antimicrobial Drugs, Viruses, and Epidemiology

Chapter 10: Controlling Microbial Growth in the Body: Antimicrobial Drugs

Chemotherapeutic Agents and Antimicrobial Agents

Chemotherapeutic agents are chemicals used to treat diseases, including infections caused by microorganisms. Antimicrobial agents are a subset of chemotherapeutic agents that specifically target microbes.

• Chemotherapeutic agent: Any drug used to treat disease in the body.

• Antimicrobial agent: A type of chemotherapeutic agent that inhibits the growth of or kills microorganisms (bacteria, fungi, viruses, protozoa).

Antibiotics, Synthetic Drugs, and Semisynthetic Antibiotics

• Antibiotic: A substance produced by microorganisms that inhibits or kills other microorganisms.

• Synthetic drug: A drug synthesized entirely in the laboratory.

• Semisynthetic antibiotic: A naturally produced antibiotic that has been chemically modified to enhance its properties.

Example: Penicillin (natural antibiotic), ampicillin (semisynthetic derivative of penicillin).

History and Timeline of Antibiotics

• Antibiotics were first discovered in the early 20th century (e.g., penicillin by Alexander Fleming in 1928).

• Development and use of antibiotics revolutionized the treatment of bacterial infections.

Mechanisms of Antimicrobial Action

Antimicrobial drugs work by targeting essential structures or functions in microbes.

• Common mechanisms include inhibition of cell wall synthesis, protein synthesis, nucleic acid synthesis, metabolic pathways, and disruption of cell membranes.

• Example: Beta-lactam antibiotics (e.g., penicillins) inhibit bacterial cell wall synthesis.

Selective Toxicity

• Selective toxicity refers to the ability of a drug to target microbial cells without harming host cells.

• Measured by the therapeutic index (ratio of toxic dose to therapeutic dose).

Antimicrobial Resistance

• Resistance occurs when microbes evolve mechanisms to withstand the effects of antimicrobial agents.

• Mechanisms include enzymatic degradation of drugs, alteration of drug targets, decreased permeability, and efflux pumps.

• Resistance can be intrinsic or acquired (e.g., via mutation or horizontal gene transfer).

Example: Methicillin-resistant Staphylococcus aureus (MRSA).

Testing Antimicrobial Effectiveness

• Common methods include disk diffusion (Kirby-Bauer) test and minimum inhibitory concentration (MIC) determination.

Multiple Resistance and Cross Resistance

• Multiple resistance: Microbes resistant to more than one antimicrobial agent.

• Cross resistance: Resistance to multiple drugs due to a single mechanism (e.g., efflux pump).

Strategies to Prevent Resistance

• Use antimicrobials only when necessary.

• Complete prescribed courses of treatment.

• Use combination therapy when appropriate.

Chapter 13: Characterizing and Classifying Viruses, Viroids, and Prions

Structure of Viruses

• Viruses consist of genetic material (DNA or RNA) enclosed in a protein coat called a capsid.

• Some viruses have an additional lipid envelope derived from the host cell membrane.

• Viral shapes include helical, icosahedral, and complex.

Viral Life Cycle

• Viruses infect host cells and use host machinery to replicate.

• Key steps: attachment, penetration, uncoating, replication, assembly, and release.

• Some viruses can integrate into the host genome (lysogenic cycle) or remain latent.

Classification of Viruses

• Based on nucleic acid type (DNA or RNA), strandedness (single or double), and replication strategy.

• Viruses are classified into families, genera, and species.

Viral Replication

• Two main cycles: lytic (results in host cell lysis) and lysogenic (viral genome integrates into host DNA).

• Animal viruses may enter cells by endocytosis or membrane fusion.

Viruses and Cancer

• Some viruses (oncoviruses) can cause cancer by disrupting normal cell regulation.

• Examples: Human papillomavirus (HPV) and cervical cancer; Epstein-Barr virus and Burkitt's lymphoma.

Prions

• Prions are infectious proteins that cause neurodegenerative diseases (e.g., Creutzfeldt-Jakob disease).

• They lack nucleic acids and propagate by inducing misfolding of normal proteins.

Chapter 14: Infection, Infectious Diseases, and Epidemiology

Normal Microbiota and Pathogenicity

• Normal microbiota: Microorganisms that reside on or in the body without causing disease.

• Opportunistic pathogens: Normally harmless microbes that can cause disease under certain conditions.

Portals of Entry and Transmission

• Pathogens enter the body via specific portals (e.g., skin, mucous membranes, parenteral route).

• Transmission can occur via direct contact, fomites, vectors, or airborne routes.

Koch's Postulates

• Set of criteria to establish a causative relationship between a microbe and a disease.

• Steps include: association with disease, isolation in pure culture, reproduction of disease in a healthy host, and re-isolation.

Virulence Factors

• Traits that enhance a microbe's ability to cause disease (e.g., toxins, adhesins, capsules).

Types of Infectious Diseases

• Acute: Rapid onset, short duration.

• Chronic: Slow development, long duration.

• Latent: Pathogen remains inactive for a period before causing symptoms.

Nosocomial and Iatrogenic Infections

• Nosocomial infections: Acquired in healthcare settings.

• Iatrogenic infections: Result from medical procedures.

• Both are significant concerns for infection control.

Epidemiology

• Study of the distribution and determinants of diseases in populations.

• Types include descriptive, analytical, and experimental epidemiology.

• Incidence: Number of new cases in a given time period.

• Prevalence: Total number of cases at a given time.

• Public health: Involves surveillance, prevention, and control of diseases.

Table: Comparison of Nosocomial and Iatrogenic Infections

Type of Infection	Definition	Example
Nosocomial	Acquired in a hospital or healthcare facility	Urinary tract infection from catheterization
Iatrogenic	Resulting from a medical procedure	Infection after surgery due to contaminated instruments

Key Epidemiological Terms

• Reservoir: Natural habitat of a pathogen.

• Vector: Organism that transmits pathogens between hosts.

• Fomite: Inanimate object that can transmit infectious agents.

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard microbiology curricula.